3.2. The genitive ending *oso- (Skt. asya,Gr. οιο,Arm. oy,13 etc.) of the nominal o-stems has been taken over from the pronominal declension. It is basically restricted to Indo-Iranian,Greek and Armenian and has been interpreted as either a dialectal Indo-European innovation or a morphological isogloss.14 Given the appearance of this genitive singular ending in Italic (osio in early Faliscan inscriptions and in one early Latin inscription, the Lapis Satricanus, c.490 bc, and in the name Mettoeo Fufetioeo) and Celtic (oiso in three or four Lepontic inscriptions from before 400 bc), it is now possible to argue that the spread of a genitive singular*ī took place relatively recently, not much earlier than the period of Italo-Celtic unity. It has been argued that the ending *os o- was also present in Anatolian. As an archaism it cannot, therefore,be used as an isogloss. Nevertheless, it is somehow significant that, as in case of the eaugment,Armenian sides with Greek and Indo-Iranian in having *os o- as a specific genitive marker of ostems.15

3.3. A commonly cited morphological feature found in Armenian, Greek and Indo-Iranian(and perhaps also Celtic) is the instrumental marker *b i(s). Furthermore, Greek and Armenian share the use of *b i- as the instrumental singular marker, probably due to extension of the athematic instrumental plural marker *b is that is also shared by Indo-Iranian. After a lengthy discussion, however, Clackson (1994: 68–74, 87) concludes that the two languages are likely to have made independent developments and denies the significance of this isogloss. He does admit the importance of this feature, however, for the dialect group Armeno-Graeco-Indo-Iranian.16

3.8. The *n-presents (see the previous paragraph) and a few other Graeco-Armenian isoglosses are treated by Clackson (1994: 74–87) as ambiguous with respect to the question of whether they represent shared innovations or independent developments: the suffix *olā-in Greek όλης (e.g. μαινόλης ‘raving, frenzied’) vs. the Armenian quasi-participles in oł,the usage of the PIE verbal suffix *s <- (Greek σκ-in Ionic iteratives and c‘-in the Armenian aorist) with restriction to past time, peculiar verbal reduplication seen e.g. Gr. δαιδάλλω ‘to embellish’ and Arm. cicałim ‘to laugh’, etc. Naturally, one should welcome such a sound and cautious approach.However, the cumulative strength of these morphological (and a few phonological) features and a great number of such lexical agreements gives additional weight to the evidence.